I want to use an image as a header background in a fluid layout. Should I have the image size set to a percentage? Or should I set the size of the image and let the borders be percentages to keep it in the same place?

it depends on the image itself. is it an image that looks good when it repeats? if it's a nicely seamed tile image, you should set the width of your header div as a percentage, not the width of the image or the borders.

Actually the image is a "shadow" box of sorts, I am trying to utilize graphics to make a "template" for a clothing store. Just an experiment or exercise to improve my self. I don't believe the image would look good repeating.

I have set the header to a specific px width and height but used % to place it.

Thanx for the advice I am sure it will come in handy.